The present invention relates to a new and improved construction of a vacuum switch having a switch housing within which there are axially arranged switching elements and fixedly mounted sheet metal electrodes, wherein between the axially aligned sheet metal members of such electrodes there are left free gaps or spaces and the confronting electrode end faces serve to take-up the base points of the arc.
Arc electrodes of the aforementioned type composed of sheet metal have been disclosed in Swiss Pat. No. 528,548 and the Swiss patent of addition 531,784 and, in contrast to conventional ring-shaped, for instance slotted circular tracks arranged at the switching elements, possess the advantage that between two of the same the switching arc also burns in a diffuse manner above approximately 10 kA cut-off current. When carrying out a cut-off operation with arcs, even with scattered or diffused arcs, metallic vapors are formed which must be removed as quickly as possible out of the switching path after extinguishing the arc in order to prevent breakdown of the switching path, for instance with recurrent voltages. In order to re-establish the dielectric state, the metallic vapors are condensed at walls of a switching element in vacuum switches, and to guarantee for sufficiently rapid condensation care must be taken to insure that the condensation surfaces come to lie in close proximity to the vapor outlet locations.
Thus, for instance, in German patent publication No. 1,207,989 there is taught to the art a vacuum switch for alternating currents wherein there is provided at a fixed switching element and at a movable switching element a respective slotted ring-shaped circular track serving as the arc electrode and between the circular tracks of the switching elements there is provided a ring which is slotted at both end faces. In this instance the switching elements are constructed such that the arc, due to magnetic effects, is propelled outwardly to the circular tracks, and the intermediate ring brings about a subdivision of the arc into partial arcs. Owing to the relatively slight spacing of the switching elements from the circular tracks and the intermediate ring as well as the intermediate ring from the circular tracks in this case there are provided favorable conditions for rapid condensation of the metallic vapors distributed over the switching path. In the case of sheet metal or plate electrodes in accordance with the teachings of the aforementioned Swiss patents the condensation of the metallic vapors is particularly good, but even with such sheet metal electrodes small quantities of metallic vapor still can move back into the separation path which, under certain circumstances, can initiate re-ignition of the arc. In order to prevent such there is provided, in addition to the sheet metal members or plates in the arc electrode, a condenser for the condensation of the metallic vapors, as such has been taught for instance in Swiss Pat. No. 554,595, granted Aug. 15, 1974 and the corresponding United States application, Ser. No. 502,396, filed Sept. 3, 1974, and now abandoned, the disclosure of which is incorporated herein by reference. With such constructed vacuum switching element having a vacuum-tight or sealed housing, a fixed switching element mounted at one housing cover and a movable switching element mounted at another housing cover, then each switching element is, for instance, surrounded by an arc electrode consisting of radially directed sheet metal members, wherein such sheet metal members are arranged for instance at a tubular element serving as the electrode support and secured to a housing cover. Further, in this arrangement the internal compartment or space of the tubular element between the housing cover and the electrode sheet metal members is filled with, for instance, metal sponge or metal shavings or chips serving as the condenser. The strict division into switching elements and arc electrodes makes it possible to optimally construct both components in accordance with their function and for the fabrication thereof to use materials (alloys) by means of which there can be extensively prevented welding at the contact elements. Furthermore, at the arc electrodes a rapid extinguishing of the arc is ensured, which as is known cannot be obtained with one material.
In a vacuum switch element the switchable current intensity is essentially governed by the construction of the switching elements and the voltage or electric strength by their separation distance. With increasing separation distance the electric strength (amplitude of the arcing or flashover voltage) does not increase proportionally, rather increases less rapidly, so that already for practical and operational reasons the electric strength of a vacuum switching element cannot be randomly increased. For switching high voltages generally therefore the same switching elements are connected in series and the series switching elements have connected in parallel therewith control elements (resistors, capacitors) in order to uniformly distribute the transient voltage at the individual partial paths. However, such series connection of the switching elements is complicated and unacceptably expensive.
Therefore, as taught, for instance, in Swiss Pat. No. 409,056 a number of contact pairs in the form of a column are arranged in a vacuum-tight housing and for the actuation of the movable contacts there is provided a common ceramic shaft. Further, between the individual contact pairs there are provided sheet metal members forming compartments which only possess one opening for the throughpassage of the ceramic shaft, in order to prevent the passage of metallic vapors from one compartment into the other. To this end there are known different constructional embodiments. Thus, for instance, there are known high voltage-vacuum switches with series arranged contact elements which in the closed position of the switch form a conductive path leading to all contact elements and in the open position of the switch form a series of interruption spaces or compartments, wherein, as taught in German patent publication No. 2,163,900, through the use of screening means which are arranged at the contact elements the interruption compartments are separated from one another and there is prevented the spreading of field lines over more than one interruption compartment. What is disadvantageous with this or similar high voltage-vacuum switches is the fact that the electrodes taking-up the arc base points also serve as contact elements and thus, consistent with the preceding explanations, there cannot be simultaneously realized good extinguishing of the arc and there cannot be rendered more difficult welding of the contact elements or pieces, because the measures necessary to prevent welding impair the characteristics responsible for the extinguishing of the arc. Therefore, under certain circumstances it can happen that a number of contacts weld together, and owing to this possibility there must be available in any case a relatively large drive energy in order to separate the welded contacts. This requires compromise solutions, especially in the case of switches operating with high-currents, and with which there also cannot be eliminated operational disturbances due to welded contacts even with non-optimum extinguishing characteristics, so that the advantage of a short separation path which is attained for the drive of such switches considerably loses in significance.